Protein Sorting Flashcards
List some of the organelles which receive proteins from the Cytosol.
Mitochondria, chloroplasts (plants), peroxisomes, interior of the nucleus
List some of the organelles which receive proteins indirectly from the ER.
Golgi Apparatus, Lysosomes, Endosomes, Inner Nuclear Membrane
Where does the vast majority of proteins synthesis begin?
Ribosomes in the Cystosol
Some are on ribosomes in the mitochondria or chloroplast?
What directs a newly synthesized protein to to the correct organelle?
The Sorting Signal in its amino acid sequence.
What happens to a protein that does not contain a sorting signal?
It remains in the cytosol permanently.
How are proteins transported across the nuclear membrane?
Via the nuclear pores
How are the proteins destined for the ER, peroxisome, mitochondria and other membrane enclosed organelles, cross their target organelle’s membrane?
They cross via “protein translocators”
What is different about a protein translocator and a nuclear pores.
Proteins can pass through nuclear pores without unfolding, while protein translocators may require that the protein unfold and “snake” in.
How do proteins with destinations beyond the ER arrive at their target?
Transport Vessicles
From where do proteins enter peroxisomes?
ER and Cytosol
What is the most common and widely studied protein that forms a “coat” around budding vesicles?
Clathrin
Describe the 4 steps of clathrin coated vesicle formation. (After the cargo molecules have been trapped by the cargo receptors)
- Clathrin coats a pit forming in the plasma membrane
- As the pit deepens, the protein dynamic pinches it off
- The pinched off vesicle pit reforms into a coated vesicle
- The vesicle sheds the clathrin coat and is now a “naked” transport body vesicle.
What role does adaptin play in transport vesicle formation?
Binds clathrin coat to the vesicle membrane and helps the cargo receptors select specific cargo molecules
What are the different types of protein complexes? What are protein complexes?
- COPII - ER to Golgi
- COPI - Golgi to ER and within the Golgi
- (AP)-Clathrin
They are different types of proteins formations that coat vesicles during transport. Each one is unique to a certain general path through the cell.
What does SNARE stand for
Soluble NSF attachment protein receptor
What are the two major proteins involved in vesicle docking?
Rab Proteins, and SNAREs
What is the function or a Rab Protein?
Binds to a corresponding tethering protein on the Cytosolic surface of a Transport Vesicle’s target. (This is a selective process and will only happen if the 2 proteins are compatible)
What is the purpose of SNARE proteins?
The t-SNARE on the target membrane binds to the v-SNARE on the transport vesicles to firmly lock the vesicle in place. Also catalyzes membrane fusion.
The protein coat on a particular vesicle is comprised of Clathrin and Adaptin 1. What are the vesicles possible and destinations origin sites for this vesicle?
Origin: Golgi Apparatus
Destination: Lysosomes via endosomes`
The protein coat on a particular vesicle is comprised of Clathrin and Adaptin 2. What are the vesicles possible and destinations origin sites for this vesicle?
Origin: Plasma Membrane
Destination: Endosomes
The protein coat on a particular vesicle is comprised of COP proteins. What are the vesicles possible and destinations origin sites for this vesicle?
Origin: ER, Golgi Cisterna, or Golgi Aparatus
Destinations: ER, Golgi Cisterna, or Golgi Aparatus
If a protein that is designed to remain in the ER escapes to the GA, how is it returned?
The ER Retention signal sequence redirects it to the ER
What are chaperone proteins?
They bind to misfolded to prevent them from exiting the ER until they fold or assemble correctly.
How do chaperones cause Cystic Fibrosis?
A slightly misfolded, yet still viable, protein caused by CF is retained by chaperone cells before it can reach its destination.
What is the unfolded protein response?
A response to accumulation of misfolded proteins held by Chaperones that causes the cell to produce more ER, Chaperones, and other quality control proteins
If the unfolded protein response is unable to keep up with protein demand, how does the cell respond?
The UPR will direct the cell to undergo apoptosis and “self destruct”
What is the difference between the Constituitive exocytosis pathway and the Regulated exocytic pathway?
Constituitive:
- Continuous in all eukaryotic cells
- Does not require signal sequence for entry
- Supplies the membrane with proteins and secretes other proteins in the process
Regulated:
- Only occurs in cells specialized for secretion (i.e. Secretion of hormones, enzymes, or mucus)
- Proteins in this path are stored in secretory vesicles until an extracellular signal triggers their secretion.
In Phagocytosis, how are the engulfed particles digested once they become phagosomes?
They fuse with lysosomes
How are fluids and some macromolecules taken into the cell?
Pinocytosis
What is pinocytosis?
The continuous process of a cell “swallowing” part of its membrane along with small amounts of extracellular fluid.
By what process does the cell take up specific molecules from the extracellular matrix? Explain the mechanism.
Receptor-mediated endocytosis
When a molecule attaches to it’s specific receptor on the membrane the membrane forms a clathrin vesicle around it and transports it to an endosome.
The endosome delivers the molecule to a lysosome, and returns the receptor to the plasma membrane
Why are nuclear import receptors necessary for nuclear proteins to pass through the nuclear pores?
The import receptor deactivates the web of proteins inside the pore that would otherwise block passage.
